A phospholipid: diacylglycerol acyltransferase (PDAT) has biochemically been characterised in yeast and plants and a gene, LRO1, encoding the PDAT enzyme was identified in yeast (Dahlqvist et al., 2000, PNAS 97:6487-6492). The enzyme was shown to catalyse the formation of triacylglycerols (TAG) by an acyltransfer from phospholipids to diacylglycerols (DAG). Furthermore, the enzymatic activity was found to be localised in the microsomal fraction. The gene encoding the PDAT enzyme was shown to have sequence homologies to the lecithin: cholesterol acyltransferase (LCAT) gene family. The LCAT enzyme is used for the treatment of LCAT deficiencies, such as arteriosclerosis by increasing the activity of LCAT in serum of the mammal to a level effective to decrease the accumulation of cholesterol (WO9717434). The diet habit used by large groups of people today result in high cholesterol values with all other problems, which follow.
Lipases are enzymes that are primarily responsible for the hydrolysis of glycerolipids such as triacylglycerols. However, it is well known that lipases also under certain conditions in water free systems, can catalyse interesterification (Gandhi, 1997, J Am Oil Chem Soc 74 (6): 621-634). The wide berth for employment in a variety of reactions and broad substrate specificity has rendered the lipases to be very useful in a variety of applications such as production of pharmaceuticals, cosmetics, detergents, foods, perfumery, and other organic synthetic materials. One example is the use of an immobilised lipase for the synthesis of waxes (U.S. Pat. No. 4,826,767 and U.S. Pat. No. 6,162,623). The low stability, low activity or selectivity encountered occasionally with a number of these enzymes have been the chief obstacle hindering a more rapid expansion of industrial lipase technology into new applications on a large scale.
Additionally, mass-production of waxes have been performed by culturing microorganisms, together with fatty-acids, wherein acyltransferases present within the microorganism convert the fatty acids into waxesters, such as by using the microorganism Staphylococcus lentus (JP 1320989). Another example is the use of Arthrobacter ceroformans for the production of waxesters (Koronelli et al., 1979, Vestn. Mosk. Univ. Ser 16, Biol 3:62-64). Other examples are the use of transgenic hosts harbouring a gene encoding an acyltransferase for the production of waxes, as described in WO 9310241 and U.S. Pat. No. 5,445,947.
Industrial application using the above mentioned lipases as biocatalyst, for the production of a variety of waxesters, is limited to the group of lipases and the restrictions these enzymes have both regarding the products that could be produced and the conditions by which these enzymes are active. For example, the esterification must occur in water free solvents and under reduced pressure.
By the use of microorganisms there are limitations such as the need of several purification steps after the synthesis of the waxesters to be able to remove the microorganism and other impurities, which comes along with the culturing method. There are also difficulties in obtaining high yields of the waxesters. The microorganism may be one that naturally encodes enzymes suitable for the synthesis of waxesters, or a genetically modified microorganism, which by the modification obtains the ability to produce waxesters.
Furthermore, the waxesters that can be synthesised today are limited due to the substrate specificity of the enzymes catalysing the wax ester synthesis in these microorganisms. Moreover, these enzymes are integral membrane enzymes, which render it impossible to use such enzymes as biocatalyst in a cell free system such as in an industrial reactor.
There is a need for new improved enzymes, which enables the production of variety of fatty acid esters to high yields in cost-efficient industrial processes. Examples of fatty acid esters are structured glycerol fatty acid esters such as triacylglycerols with a specific acyl group at the sn2 positions that differs as compared to that of the outer positions and diacylglycerols with specific acylgroups. Production of fat-soluble fatty acid esters by acylation of water-soluble molecules, such as flavours and vitamins, is another example of desirable fatty acid esters. Other valuable fatty acid esters of interest are waxesters (i.e. fatty acids esterified to long chain alcohols), or fatty acid esters of molecules such as carbohydrates and amino acids. A method for the production of such compounds can be achieved by optimising enzymes that already is used as biocatalyst exemplified by the well-known families of lipases or other membrane independent enzymes. However, in nature many of the enzymes catalysing the transfer of acylgroups are integral membrane proteins. Among the membrane independent acyltransferases present in nature the vast majority catalyses an acyl-CoA dependent reaction. Both these classes of acyltransferases are not suited as a biocatalyst in industrial methods since integral membrane protein are not functioning in cell free systems and acyl-CoA is a to costly substrate. Furthermore, in applications involving enzymes belonging to the lipase family the interesterification is dependent on a water free system. Hence, membrane independent acyltransferases that could use acyl-lipids as acyl donors in industrial methods for the manufacturing of fatty acid esters are limited today and no such enzyme is available which can manufacture several different fatty acid ester and/or fatty acid thioesters, i.e., use a lot of different acyl donors and acyl acceptors.
There are also needs for enzymes to be used to improve the properties of complex raw material. For example within the area of food production, modification of different components such as lipids present in food raw material such as milk cereals, vegetables, eggs, vegetable oils, meat, fish, etc is desirable. Examples of improvements achieved by such modifications are enhanced emulsifying properties, increased shelf life, less off-flavour, etc. For example in many food applications enhanced emulsifying properties are desirable and can be achieved by converting phospholipids (i.e. lecithin) present in the food raw material into lysophospholipids. Lipases are commonly used in such applications resulting in elevated levels of lysophospholipids but also unesterified fatty acids that can result in off-flavours. Conversion of phospholipids into lysolipids without increased amounts of unesterified fatty acids is therefore desirable and can be achieved with acyltransferases that transfer the fatty acid from the phospholipid to an acyl acceptor such as monoacylglycerols, diacylglycerols, alcohols, or any other acyl acceptors present in or added to the raw material.